Nigeria had ordered a sound investment (7,3)
I believe the answer is:
hearing aid
'a sound investment' is the definition.
(something helping someone to hear sound)
'nigeria had ordered' is the wordplay.
'ordered' indicates an anagram.
'nigeria'+'had'='nigeriahad'
'nigeriahad' is an anagram of 'HEARING-AID'.
(Other definitions for hearing aid that I've seen before include "Amplifier for ear" , "Ear trumpet" , "Help for the partially deaf" , "Earpiece" , "asset in court?" .)